Electroacoustic transmitter and the like



Feb. 3, 1942.. D. o. SPROULE 2, 7

ELECTROACOUSTIC TRANSMITTER AND THE LIKE Filed May 1, 1959 2Sheets-Sheet l !//z a g Dona\d sproum vEN-roQ Feb. 3, 1942. D. o.SPROULE 2,271,667

ELECTROACOUSTIG TRANSMITTER AND THE LIKE Filed May 1, 1939 2Sheets-Sheet 2 J K y c &

Patented F ch. 3, 1942 ELECTROACOUSTIC TRANSMITTER AND THE mm.

Donald Orr Sproule, London, England, assignor of one-third to ArthurJoseph Hughes, Essex, England, and one-third to Henry Hughes & SonLimited, London, England, a British com- 7 Application May 1, 1939,Serial No. 271,025

In Great Britain May 4, 1938 7 Claims.

This invention relates to electro-acoustic transmitters and the like andhas for one object to form a structure which can be magnetised rapidlyand strongly and which can be demag- I netised rapidly.

Another object of the invention is to form a magnetic structure in whichthe magnetising flux can be built up in the magnetic circuit veryrapidly and, to a considerable extent free from the delaying action ofeddy current in the magnetic material thus enabling echo soundingtransmitters to be constructed in which the polarising coil may beenergised very powerfully but only intermittently.

A further object of the invention is to form an electro-acoustictransmitter or the like in which the length of the magnetic circuit isreduced, the density of the magnetising electric current can beincreased and the dimensions andinductance of the magnetising coil maybe made less than is usual with known constructions.

Owing to the conditions and circumstances of use it is most importantthat the utmost economy of space, weight and cost of materials should beexercised thus making it undesirable if not quite impracticable toemploy a permanent magnet in such transmitters also the ordinary form ofelectromagnet is unsuitable when it is required to energise suchelectromagnet only for that time during which the driver coil is beingenergised as the solid construction prevents a rapid rise and fall ofthe field strength in the gap and the high inductance of the windingsprevents the necessarily rapid rise in current that is called for if themagnetic field strength is to be raised rapidly.

An additional object of the invention is to en able a very robust andpowerful electro-acoustic transmitter to be constructed suitable forecho sounding and similar purposes which can be operated moreeconomically than known transmitters for the same purpose.

The invention consists of an improved electro-acoustic motor having astationary electromagnet with a polar gap for a driver coil and apolarising coil characterised in that the electromagnet core is composedof laminations of magnetic material insulated from one another.

The invention can be put into practical effect by many diversconstructions and arrangements so that the following description must beconsidered as of one example only.

In the drawings- Fig. 1 is a front elevation of one kind of laminationused in the construction.

Fig. 2 is a front elevation of another kind of lamination used in theconstruction.

Fig. 3 is a part sectional perspective'elevation showing a stage ofassembly.

Fig. 4 is a part sectional perspective elevation showing the assemblycompleted. a

Figure 5 is a fragmentary plan view drawn to a larger scale partly insection and with parts broken away to expose underlying features;

Figure 6 is an elevation of one form of improved electro-acoustictransmitter arranged according to this invention.

As shown in Figure 4 a radial cross sec- 7 tion through the improvedconstruction exhibits a pot magnet A having a tunnel a for a polarisingcoil b, a polar gap c for a driver coil and angular surfaces d and e forcooperation with the base plate I and ring g.

The improved pot magnet A is composed of la'minations of magneticmaterial which are arranged radially or substantially so and which areof such parallel or taper transverse section that they can cooperatewith insulating material and/or spacers interposed therebetween to becompacted into annular foim..

To enable the polarising coil b to be located in the tunnel a, the potmagnet structure A consists of two series of laminations, an innerseries of laminations h (Figure 1) substantially of rectangular form andnotched on the lower part to produce the angular surface d and an outerseries of laminations (Figure 2) substantially of channel shape to formthe tunnel a between the limbs k and l when associated with a laminationh as shown in Figure 4. Each lamination j is notched to produce anangular surface eand the radial length of the limb is is less than thatof the limb I so that the gap 0 is formed when the parts are assembled.

The individual laminations h and i are composed of magnetic materialwith an insulating layer and may be stamped from ordinary flat sheet, thsaid laminations being assembled radially or substantially so. Aseachlamination h or a is substantially of equal thickness when out from aflat sheet if they are arranged radially it is necessary to introducespacers m of paper in the gaps non the external peripheries as shown inFigure 5 to enable consolidation to be effected. Alternatively the useof the spacers m may be avoided if the individual insulated laminationsare slightly curved so as to increase the effective thickness of eachlamination h, or :irelatively to the increase in radius, or some or allof the laminations h or 7' are given a wedge shaped cross section.

The construction shown in the drawings includes the circular base plateI having an internally arranged annular flange o presenting an angularsurface 12 externally and a threaded outer periphery q for cooperatingwith the screwed ring 9 having an internal angular surface 1'.

During assembly, as shown in Figure 5 the inner series of insulatedlaminations h and paper spacers m is arranged on the base plate 1 withthe angular parts d in contact with the angular surface p of the annularflange o, the polarising coil b is placed in position and the outerseries, of insulated laminations a and paper spacers m is arranged onthe base plate f over the coil b with the internal faces of the lowerlimbs l in contact with the external surface of the inner series, thescrewed ring 9 is then placed in position and tightened up to clamp theassembly of stampings' h and 7, the spacers m and the coil b firmly inplace and with the laminations insulated from one another.

The whole assembly may be impregnated withshellac, artificial resin,condensation product, or other insulating natural or artificialsubstance or composition to increase the rigidity of the structure andusually is attached to the remainder of'the electro-acoustic apparatusbyscrews or the like as shown in Figure 6.

It will be recognised that by the use of a laminated structure for thepot magnet A the delaying action of eddy currents is avoided and that.

it is possible toenergise thepolarising coil 1) intermittently by anelectrical current of higher density than is possible or convenient whencontinuous energisation is efiected thereby enabling the size of thepolarising coil 1) to be reduced and the length of the magnetic circuitto be shortened with a consequential reduction of the magneticreluctance so that it is possible to use a relatively small number ofampere turns having a comparatively low inductance.

The so called driver coil s located in the gap 0 may be of the usualwire wound form or may consist of a solid metal ring in which theexciting current may be induced by transformer action from thepolarising coil b supplied with an energising alternating current forthis purpose in addition to the pulses of direct current for polarising,thus reducing the supply conductorsv to a single'two core cable, saidsolid metal ring having very much greater strength. than a coil of wiresuch as s wound on a former t so that it is better able to withstand thevery large forces to .lar series of bifurcated laminations with limbs ofunequal length arranged with said limbs disposed radially and inwardly,an annular series of rectangular laminations arranged radially and eachhaving one end in contact with a longer limb of" one of said first namedlaminations and 7 the other end spaced from the shorter limb of said oneof said bifurcated laminations to define an air gap, a polarising coilbetween said limbs, an annular driving member in said air gap, a pair ofannular members engageable with the inner edges of said rectangularlaminations and the outer edges of said bifurcated laminations to clampsaid laminations together in said annular form and interengaging meansfor detachably connecting said annular members.

2. An electroacoustic motor having an annular series of bifurcatedlaminations with limbs of unequal length arranged with said limbsdisposed radially and inwardly, an annular series of rectangularlamination arranged radially in contact with one series of lambs of saidfirst named laminations and spaced from the other series of said limbsto define an air gap, a polarising coil between said limbs, an annulardriving member in said air gap, oppositely directed inclined portions onthe outer edges of each of said laminations, and a pair of detachablyconnected annular clamping elements having inclined surface portionengaging the inclined edge portions of said laminations to retain thelatter in position.

3. An electroacoustic motor having an annular series of bifurcatedlaminations of even thickness with limbs of unequal length arranged withsaid limbs disposed radially and inwardly, wedge shaped spacers betweensaid laminations, an annular series of rectangular laminations of eventhickness each rectangular lamination being disposed radially with oneend in contact with the longer limb of one of said first namedlaminations and the other end spaced from the shorter limb of said oneof said first mentioned laminations to form an air gap, wedge shapedspacers between said laminations, a polarising coil between said limbs,an annular driving member in said air gap, an angular projection on theouter edge of each lamination, a base plate and a clamping elementdetachably connected to said 'base plate, said base plate and clampingelement said limbs disposed radially and inwardly, wedge shaped spacersbetween said laminations, an annular series of rectangular laminationsof even thickness arranged radially in contact with one series of limbsof said first named laminations and magnetically cooperating with bothseries of said limbs to form annular salient poles, wedge shaped spacersbetween said laminations, a polarising coil between said limbs, anannular driving member between said po les, an angular projection oneach lamination, an annular base plate, an annular fiange on said baseplate having an angular surface to fit the angular projections on therectangular laminations, an external screw thread on said base plate, aring, said ring having an angular surface to 'fit the angularprojections on the bifurcated laminations and an internal screw ths eadto fit the screw thread on said base plate.

5. In an electroacoustic motor, the combination of a serie of bifurcatedthin laminae having spacedapart limbs arranged in the form of an annuluswith said limbs directed radially of said annulus, a second series ofsubstantially rectangular laminaedisposedjn alignment witltsaidbifurcated laminae with one end of each lamina of said second serie incontact with one limb of each bifurcated lamina and the other endadjacent to and spaced from the other limb of said bifurcated lamina toform an air gap, relatively inclined portions on the outer edges of thelaming paced apart limbs arranged in the form of an annulus with saidlimbs directed radially of said annulus, a second series of laminaespanning the gap between and in alignment with the limbs of saidbifurcated laminae with one end of each laminae of said second series incontact with one limb of each bifurcated lamina and the other endadjacent to and spaced from the other limb of said bifurcated lamina toform an air ,gap, relatively inclined portions on the outer edges of thelamina of both series and a pair ofinterengaging members having surfacescomplementally inclined with relation to and engaging the inclinedportions on said laminae for retaining the latter in said annular form.

7. The device as set forth in claim 6 comprising a polarizing coilbetween the limbs of said bifurcated member and a driving memberdisposed in said air gap.

DONALD ORR. SPROULE.

